My invention relates to an electromagnetic friction apparatus and, more particularly, to an improved electromagnet for use in such apparatus.
Known electromagnet braking systems utilize an electromagnet affixed to a movable lever arm which actuates the brake mechanism, upon energizing of the electromagnet. When energized, the electromagnet slidingly engages a rotating armature plate, rotating with and coupled to the wheel to be braked. The rotating armature plate, consequently, drags the electromagnet in the direction of its rotation, causing pivotal movement of the lever arm which, in turn, actuates the brake mechanism.
The commonly used, flat faced, central core type electromagnets of the prior art, for example, as described in U.S. Pat. Nos. 2,304,118; 3,753,182; 3,756,355; and 3,757,264; when in sliding engagement with the rotating armature plate exhibit what is referred to as "squeal". Electromagnet squeal is believed to result from an audible vibration created by the electromagnet's leading edge gouging, or digging into, the armature plate surface, particularly upon initial electromagnet--armature plate engagement. Such gouging, or digging, of the armature plate is thought to result from the tilting moments imposed upon the magnet about the point of attachment of the electromagnet to the lever arm.
In addition to causing an undesirable squeal, the electromagnet tilting moments also cause the magnet leading edge to wear at a higher rate than that of the trailing portion of the magnet. As the leading edge wears, it forms a new tapered friction face extending from the leading edge to the point of magnet attachment to the lever arm. Because of this two plane wear the trailing half of the magnet will no longer engage the armature plate, resulting in loss of braking effectiveness.